pump fails to pump from fluid wagon

[RickJS]

Normally when a pump is lined up to a fluid wagon, mousing over the pump shows a green box (brackets?) under the wagon, next to the pump. Now I have a case where the box is red and the pump doesn't pump fluid. What am I missing?

[DaleStan]

Are there any curves in the rail between the train stop and the fluid wagon? Pumps only work if the portion of the train from the stop to the wagon is straight.

[valneq]

… and it needs to be horizontal or vertical. Straight diagonal rails do not connect to pumps. Neither do curved rails.